1. Field of the Invention
The present invention relates to a holographic memory.
2. Background of the Related Art
As large scale recording and reproduction of information is required, recently optical information recording/reproduction technologies which can make three dimensional information recording/reproduction using holography is under development other than two dimensional recording/reproduction devices using optical disk recording medium, such as CD and DVD and the like.
Referring to FIG. 1, the information recording/reproduction device using holography is provided with a laser 15 for a light source, and a beam splitter 14 for splitting a beam 16 from the laser 15 into a reference beam 6 and an object beam 7. The reference beam part is provided with in an order of a beam expander 12 for expanding a diameter of the reference beam 6, a beam deflector 11 for directing the reference beam 6 expanded by the beam expander 12 toward a telescope 9 with an 1:1 magnifying power and changing an incident angle to the telescope 9, and the telescope 9 for forming an image of a reflecting plane of the beam deflector 11 on a recording medium 103, and the object beam part is provided with in an order of a beam interrupter 17 for controlling advance of the beam, a beam expander 13 for expanding a diameter of the object beam 7, a reflector 10 for deflecting a direction of beam, an SLM(Spatial Light Modulator) 1 for displaying information, an FTL(Fourier Transform Lens) 102 for subjecting an image displayed on the SLM 1 to Fourier transform onto the recording medium 103. The recording medium 103 is positioned at a place the reference beam 6 and the object beam 7 are met, an image forming lens 4 is provided at a place a given distance away from the recording medium 103 in the direction of the object beam 7, a CCD(Charge Coupled Device) 5 is provided at an image forming plane of the image forming lens 4 for converting an image from the SLM 1 into an electrical signal, and the SLM 1 and the CCD 5 are put under the control of a computer 8.
The operation of the aforementioned holographic memory will be explained.
Upon displaying information on the SLM 8 by the computer 8 and the reference beam 6 and the object beam 7 are to the recording medium 103 on the same time, the object beam 7 and the reference beam 6 make an interference, to form an interference pattern, which is recorded on the recording medium 103. After the recording, if the object beam 7 is interrupted by the beam interrupter 17 while the reference beam 6 is directed to the recording medium 103, the reference beam 6 is diffracted by the interference pattern recorded on the recording medium 103, to reproduce the object beam 7 advancing in the direction of the CCD 5. If the object beam 7 is formed an image on the CCD 5 through the image forming lens 4, the image displayed on the SLM 1 is formed on the CCD 5, and the computer 8 stores and analysis the electrical signal from the CCD 5. Another information may be recorded by displaying the another information on the SLM 1 and changing an angle of deflection of the beam deflector 11, wherein, even if the angle of deflection is changed by the beam deflector 11, an incident angle of the reference beam 6 to the recording medium 103 is changed while the image formation of the image formation plane on the recording medium 103 is maintained the same, because the telescope 9 positioned between the beam deflector 11 and the recording medium 103 has a magnifying power of 1:1. Eventually, the reference beams 6 having slightly different incident angles and the object beam 7 form slightly different interference patterns respectively at the same position of the recording medium 3, which are recorded on the recording medium 103. Therefore, upon directing the reference beam 6 to the interference patterns overlapped at the same position, only the interference pattern formed by the reference beam 6 having the same incident angle with the reference beam 6 used in recording and the object beam 7 satisfies the Bragg condition, thereby reproducing only one object beam 7. That is, by controlling an incident angle of the reference beam 6, the object beam 7 can be reproduced, selectively.
There have been a variety of studies for increasing a recording capacity of the memory using the aforementioned holography, a related art of which is illustrated in FIG. 2. The device illustrated in FIG. 2 is the related art device shown in FIG. 1 added with beam deflectors 18 and 19 for deflecting beam in a direction perpendicular to the direction of beam deflection of the beam deflector 11, i.e., at a xz-plane. As shown in FIG. 3, in the device, the recording medium 103 is divided in z-axis direction for recording information, thereby increasing a recording capacity.
However, because the technology also utilizes the recording medium 103 only one dimensionally, the technology has a limitation in increasing the recording capacity.